It has been known to provide perfusion devices, such as oxygenators, characterized by larger or smaller membrane area and priming volume, for use on patients with larger or smaller blood volume. Pleated membrane perfusion devices are disclosed in Lobdell U.S. Pat. No. 4,163,721, "Edge Sealed Pleated Membrane", granted Aug. 7, 1979, and in Elgas et al. U.S. Pat. No. 4,451,562, "Blood Oxygenator", granted May 29, 1984, both incorporated by reference herein.